Fix another -Wsign-compare bug with GCC 4.9.2.

Fix another -Wsign-compare bug with GCC 4.9.2.

BUG=

Committed: https://crrev.com/dd0f469da3901ed6dabf84232fa41bb2fe59137b
Cr-Commit-Position: refs/heads/master@{#28498}

[paul.l..., 2015-05-20 01:58:48]

paul.lind@imgtec.com changed reviewers:
+ dusan.milosavljevic@imgtec.com, machenbach@chromium.org, ssid@chromium.org,
svenpanne@chromium.org

[paul.l..., 2015-05-20 01:58:49]

PTAL, another one like https://codereview.chromium.org/1128043002, from today's
https://codereview.chromium.org/1113233002

[Sven Panne, 2015-05-20 06:37:06]

The CQ bit was checked by svenpanne@chromium.org

[commit-bot: I haz the power, 2015-05-20 06:37:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1147923002/1

[commit-bot: I haz the power, 2015-05-20 06:37:23]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-05-20 06:37:24]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[Sven Panne, 2015-05-20 06:38:25]

The CQ bit was checked by svenpanne@chromium.org

[Sven Panne, 2015-05-20 06:38:25]

lgtm

[commit-bot: I haz the power, 2015-05-20 06:38:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1147923002/1

[commit-bot: I haz the power, 2015-05-20 07:13:15]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-20 07:13:23]

Patchset 1 (id:??) landed as
https://crrev.com/dd0f469da3901ed6dabf84232fa41bb2fe59137b
Cr-Commit-Position: refs/heads/master@{#28498}